What is a database link in oracle database?

Database link is an oracle database object that enables us to connect to other schema objects located on different databases. It enables us to query data from multiple database tables using one SQL query.

To access data from other target  databases, we have to create a database link on the source database .

Example :

CREATE DATABASE LINK "LINK_TO_TARGET_DB"
   CONNECT TO "SOURCE_DBLINK" IDENTIFIED BY VALUES ''
   USING '(DESCRIPTION=
                (ADDRESS=(PROTOCOL=TCP)(HOST='')(PORT=1521))
                (CONNECT_DATA=(SID =''))
            )';